At the time of the 31-year-old actor's death last weekend, the couple was closer than ever to tying the knot, a source tells PEOPLE. Other sources say they had been discussing marriage and were planning to walk down the aisle.
Still, another source maintains that there was never a formal engagement. But by all accounts, in the weeks prior to Monteith's trip to Vancouver, he was spending almost all of his time with Michele.
On Tuesday, in a statement via her reps, Michele, 26, extended her thanks for the outpouring of support during this devastating time.
"Lea is deeply grateful for all the love and support she's received from family, friends and fans. Since Cory's passing, Lea has been grieving alongside his family and making appropriate arrangements with them," the statement reads. "They are supporting each other as they endure this profound loss together."
Though the Glee costars hadn't been photographed in the days leading up to Monteith's shocking death, they were "happy and very in love," a different source says.
After dating for more than a year, Michele told PEOPLE that working with her real-life love was something she enjoyed.
"I love working with Cory, I always have," she said in September 2012. "He really, really inspires me, and he motivates me and I think he's just so talented. Working with him has been one of the best experiences of this whole process."
When Monteith entered treatment for substance abuse last March, Michele stood by her man and the pair reunited and relaxed in Mexico in May.
Fans of Monteith may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.